The Unit has conducted a series of projects to elucidate the rhythmic aspects of sleep, and has also participated in broader studies of biological rhythms in depressive illness. In order to determine if the circadian rhythms of temperature and sleep represent "the hands of the clock" or whether they interact on some more fundamental level, studies of sleep are being performed on subjects wearing a "space suit" on loan from NASA. Using control systems developed here, the suit can virtually abolish the circadian rhythm of temperature. In another project normals and depressed patients are placed on a 1 hour dark/2 hour light schedule to enhance the rhythmic aspects of REM sleep and determine if depressives are phase advanced in this measure.